MADRID/BARCELONA (Reuters) - The secessionist leader of Catalonia called for international mediation on Monday in the region's dispute with Madrid, a day after hundreds of people were hurt as police swung truncheons and fired rubber bullets to disrupt an independence referendum.

Results showed voters had overwhelmingly backed independence in the referendum, which Spain has ruled illegal and which opponents of secession mostly boycotted.

The vote was valid and must be implemented, said Catalan leader Carles Puigdemont.

"It is not a domestic matter," he told a news conference on Monday. He said it was "obvious that we need mediation", adding: "We don't want a traumatic break ... We want a new understanding with the Spanish state."

Prime Minister Mariano Rajoy met leaders of other political parties and his conservative government issued a statement saying he was seeking a joint response to the crisis. He also spoke to other European leaders and thanked them for supporting Spain's constitutional order, the statement said.

In Barcelona, hundreds of students gathered in a central square to protest at Sunday's police crackdown, chanting pro-independence slogans and waving Catalan flags.